The invention relates to a method for operating an internal combustion engine, especially of a motor vehicle, wherein a lean air/fuel mixture is supplied to a combustion chamber in a first mode of operation and wherein a stoichiometric or a rich air/fuel mixture is supplied in a second mode of operation. In the method, the supplied air/fuel mixture is combusted in the combustion chamber. The invention also relates to an internal combustion engine especially for a motor vehicle. A lean air/fuel mixture is supplied to a combustion chamber in a first mode of operation and a stoichiometric or a rich air/fuel mixture is supplied to the combustion chamber in a second mode of operation. The supplied air/fuel mixture is ignited in the combustion chamber and the engine has a control apparatus for controlling (open loop and/or closed loop) the two modes of operation.
A method of this kind and an internal combustion engine of this kind are, for example, known from motor vehicles having gasoline injection into an intake manifold arranged forward of the combustion chamber. There, the engine is run in idle and at part load with a stoichiometric or lean air/fuel mixture to reduce the fuel consumption and the generation of exhaust gases containing toxic substances. If the driver of the motor vehicle desires an acceleration, then the engine is driven with a rich air/fuel mixture for such a full load in order to generate the required torque for the acceleration. The control (open loop and/or closed loop) of such a gasoline injection takes place via a throttle flap with which the air mass supplied to the combustion chamber is influenced as well as via an injection valve mounted in the intake manifold. The fuel mass injected into the intake manifold is influenced by the injection valve. The air/fuel mixture, which is supplied to the combustion chamber in this way, is ignited by a spark plug and the fuel is combusted. The torque generated by the engine results from the combustion of the fuel.
Especially because of the different modes of operation, it is possible that so-called jolting can occur during the operation of the engine.
It is an object of the invention to provide a method and an internal combustion engine, especially for a motor vehicle, which exhibit as little jolting as possible or no jolting.
This object or task is solved in a method of the above-described kind in accordance with the invention in that, in a transition between the two modes of operation, the ignition time point or the ignition angle is retarded for the ignition of the air/fuel mixture. In an internal combustion engine of the kind described initially herein, the task is solved in accordance with the invention in that the ignition time point or the ignition angle for the ignition of the fuel is retarded via the control apparatus for a transition between the two modes of operation.
The throttle flap of the engine is first closed for a transition, for example, from a lean air/fuel mixture to a stoichiometric or rich air/fuel mixture so that less air mass reaches the combustion chamber. The reduction of the air mass takes place with a time delay because of the storage action of the intake manifold arranged between the throttle flap and the combustion chamber. This has the consequence that too much air mass from the intake manifold reaches the combustion chamber approximately during this time delay after the closure of the throttle flap. The stoichiometric or rich air/fuel mixture which is wanted after the transition into the second mode of operation, is thereby disturbed which is noticed by a torque increase, that is, by a jolt.
The efficiency of the combustion in the combustion chamber is deteriorated by the ignition retard of the ignition time point or ignition angle. This has the consequence that the resulting torque increase is prevented or at least reduced.
For a transition from a stoichiometric or rich air/fuel mixture to a lean air/fuel mixture, the reverse is true and the throttle flap is first opened so that a larger air mass reaches the combustion chamber. However, here too, a time delay is present because of the intake manifold until the increased air mass, which is required for the second mode of operation, reaches the combustion chamber. Too large an air mass for the first mode of operation is present during this time delay which becomes manifest as a jolt when there is a torque increase.
Because of the retardation of the ignition time point or ignition angle in accordance with the invention, the efficiency of the combustion is again deteriorated so that the jolting is at least partially or even completely diminished.
Accordingly, the ignition retardation provides that the engine exhibits no jolting or virtually no jolting in the transition between the two modes of operation. The smooth running of the engine and therefore the comfort for the driver is thereby improved.
In an advantageous embodiment of the invention, the ignition time point or the ignition angle is retarded during a transition in such a manner that the torque, which is generated by the engine, remains approximately constant during the transition.
Accordingly, for a transition from a lean air/fuel mixture to a stoichiometric or rich air/fuel mixture, for example, the occurring torque increase is precisely so balanced and compensated by the ignition retardation according to the invention that no or virtually no change of the torque, which is generated by the engine, takes place during the transition. In this way, it is achieved that no jolting or virtually no jolting is present during the transition.
In an advantageous embodiment of the invention, when there is a transition from the first mode of operation into the second mode of operation, the ignition time point or ignition angle is retarded after the transition.
Directly after the transition to the stoichiometric or rich air/fuel mixture, there is still too much air present in the combustion chamber because of the already-mentioned storage action of the intake manifold. The torque increase resulting therefrom therefore results directly after the transition into the second mode of operation. With the retardation of the ignition time point or ignition angle taking place after the transition, the compensation of the torque increase takes place at the correct time, namely, directly after the engine has transferred into the second mode of operation.
In a further advantageous embodiment of the invention, for a transition from the second mode of operation into the first mode of operation, the ignition time point or the ignition angle is retarded in advance of the transition.
With the mentioned delaying action of the intake manifold, there is too much air already present in the combustion chamber in advance of the transition to the lean air/fuel mixture. The torque increase, which results therefrom, therefore takes place directly in advance of the transition into the first mode of operation. With the retardation of the ignition time point or ignition angle starting in advance of the transition, it is achieved that the compensation of the torque increase takes place at the correct time, namely directly before the engine goes over into the second mode of operation.
In an advantageous embodiment of the invention, the fuel mass is reduced when there is a transition between the two modes of operation.
A reduction of the generated torque and therefore a reduction of the torque increase during the transition between the first and second modes of operation can be achieved by the reduction of the fuel mass. In this way, a jolting of the engine can, if required, be completely or at least partially prevented by this reduction of the fuel mass. It is thereby possible to substitute the retardation of the ignition time point or ignition angle in accordance with the invention, if required, completely or at least partially with the reduction of the fuel mass.
Preferably, the reduction of the fuel mass takes place additionally to and approximately simultaneously with the retardation of the ignition time point or ignition angle. In this way, it is no longer necessary to compensate the entire torque increase by the retardation so that, in comparison to a compensation without a reduction of the fuel mass, a lesser retardation is sufficient. This affords the advantage that an error in the computation of the retardation of the ignition time point or the ignition angle has a lesser effect on the efficiency of the combustion and therefore on the compensation of the torque increase.
An especially advantageous embodiment of the invention provides that the fuel is injected directly into the combustion chamber of the engine during a compression phase in the first mode of operation.
It is then further advantageous when the fuel is injected directly into the combustion chamber during an induction phase in the second mode of operation.
Accordingly, the above-mentioned especially advantageous embodiment of the invention is a so-called gasoline direct injection wherein the fuel is injected in each case directly into the combustion chamber of the engine with an injection valve in contrast to the previous intake manifold injection of the fuel. To reduce the fuel consumption and the generation of exhaust gases which contain toxic substances, a lean air/fuel mixture is achieved in the first mode of operation in that the fuel is injected into the combustion chamber in the compression phase of the engine. This first mode of operation is also called stratified operation or stratified charge operation. In the second mode of operation (as in the intake manifold injection), the fuel is injected into the combustion chamber during the induction phase. This can be a stoichiometric or rich air/fuel mixture with which especially the required torque is generated, for example, for an acceleration of the vehicle. This second mode of operation is also called homogeneous operation.
In the gasoline direct injection described, it is especially advantageous when there is a switchover between the two modes of operation especially via a control apparatus. The switchovers take place in dependence especially upon the driver command and the operating variables or state parameters of the engine.
With the application of the retardation of the ignition time point or ignition angle in accordance with the invention on the gasoline direct injection, it is achieved that no jolting or at least virtually no jolting is present in the there present switchovers from the stratified operation into the homogeneous operation and vice versa. The invention thereby effects an improved smooth running of the engine and thereby an improved comfort for the driver of the motor vehicle.
The realization of the method of the invention in the form of a control element is of special significance and this control element is provided for a control apparatus of an engine, especially of a motor vehicle. A program is stored on the control element which can be run on a computing apparatus and especially on a microprocessor and is suitable for carrying out the method according to the invention. In this case, the invention is therefore realized by a program stored on the control element so that the control element provided with the program defines the invention in the same way as the method for which the program is suitable for carrying out. As a control element, especially an electrical storage medium can be used, for example, a read-only-memory.
Additional features, application possibilities and advantages of the invention will become apparent from the subsequent description of the embodiments of the invention which are shown in the drawing. Here, all described or illustrated features define for themselves or in any desired combination, the subject matter of the invention independently of their description in the patent claims or their reference as well as independently of their formulation or illustration in the description or in the drawing.